This invention concerns improvements relating to drivable load-carrying rollers, particularly rollers for so-called accumulating conveyors. In such conveyors, a usual requirement is that it should be possible for a group or groups of rollers, or individual rollers, to be disconnected from driving means when so required, for example for automatically removing the drive from a group of rollers in dependence upon the detected condition of occupation by a load or loads on a group of rollers downstream from the first-named group and thereby limiting pressure upon that load or loads of following loads. For this purpose, comparatively complex and expensive arrangements have been heretofore proposed. The present invention seeks to provide a simpler arrangement which is also economic and safe.